The present invention relates generally to equipment--especially, portable routers and the like--for forming shaped edge profiles on sheets of material such, for example, as the edges of aluminum sheets, in those regions where two of such sheets are intended to be abutted and welded together; yet, for insuring that the root face thickness of the shaped sheet edge--i.e., that portion of the shaped edge from which no material is removed--remains of constant thickness irrespective of thickness variations within any given sheet and/or from sheet-to-sheet, and wherein such improved shaped edge profiles can be quickly and easily formed even by unskilled operators on a consistently reproducible basis.
In the formation of many types of fabricated products such, merely by way of example, as aircraft, missiles, ships, tanks, vehicles, containers, etc., it is often necessary to abut two sheets of material in edge-to-edge relation and to weld such sheets together, preferably forming a welded seam which, in cross-section, is of essentially the same thickness as the sheet material itself. To accomplish this, it has been a common practice to pre-shape the sheet edges by, for example, routing. Unfortunately, however, prior to the advent of the present invention, this has commonly involved the use of routers or other portable edge preparation machines which index to the side or face of the sheet from which the material is being removed--i.e., the sheet face closest to the welder. Since the thickness of such sheets will inherently vary (both within a given sheet and from sheet-to-sheet), the result has been that the root face thickness of the thus shaped edges also vary. Stated differently, because the routing tool is indexed from the sheet face from which material is to be removed, the routed channel thus formed will have a constant depth and, since the thickness of the base metal sheet varies, the root face thickness at the shaped edge must also vary. This has inherently resulted in significant problems when attempting to weld such sheets together since the root face thicknesses of the two abutting edges are not constant and identical.
Typical examples of prior art approaches to routing processes and equipment, especially for edge preparation of sheet materials, are those disclosed in, for example, the following U.S. Pat. Nos. 3,853,160--Posey; 4,024,898--Bergler et al; 3,893,372--Strakeljahn; 3,212,541--Burrows et al; 2,935,102--Potter; 2,839,107--Emmons; and, 2,672,898--Schuster. For example, in the aforesaid Posey U.S. Pat. No. 3,853,160, the patentee is concerned with forming a step or ledge in a workpiece edge; and, as in the other patents noted above, provides a router or similar edge preparation machine which is indexed from the edge or face of the workpiece from which material is being removed. As a consequence, any variations in thickness of the workpiece are replicated in the root face thickness since the step 16 remains of uniform depth with respect to the surface 26 from which the routing tool is indexed. See, e.g., Posey U.S. Pat. No. 3,853,160, Col. 2, 11. 51-57.